Broadband microwave point contact rectifier



April 14, 1959 c. E. WEAVER ET AL 2,882,466

BROADBAND MICROWAVE POINT CONTACT RECTIFIER Filed-March 5, 1957 F9 E A United States Patent v'BROADBAND MICROWAVE POINT CONTACT RECTIFIER Carson E. Weaver and John G. Hambor, Bethlehem, Pa., :assignors to Gahagan, Inc., Esmond, RJ., `a corpora- .tion of Pennsylvania Application March 5, 1957, Serial No. 644,158

'Claims. (Cl. 317-236) This invention Arelates topoint contact rectifiers, and vmore 'particularly to a point contact rectifying unit of the typeemploying the combination of a body of semicon- 'ductor inaterial, such as a piece of germanium crystal "and a metallic pointed wire element'which engages the fsurfaceof Athe semiconductor material.

A mainobject of the invention is to provide a novel -and improved point contact rectifier unit which is simple -:in construction, which is easy to manufacture, and which provides efiicient operation 4throughout a substantial portion of the `radio frequency spectrum, namely, `Vthrough the portion of the I'radio frequency spectrum from 1,000 `megacycles per second to 10,000 megacycles `per second '-A '-further object of the invention is to provide an improved point contact rectifier of the germanium crystal type, said rectifier being relatively inexpensive to manurfacture, being rugged in construction, and being especially adapted for use in the portion of the radio frequency l-sp'ectr'urn from 1,000 megacycles per second to 10,000 megacycles per second,`the improved rectifier unit providing efficient performance with low noise and with relatively rhigh sensitivity.

xA`tstill further object of the invention is to provide -ant-improved'pointcontact rectifier unit of thegermanium scrystal type which is designed to demodulate radio frequency signals in the spectrum range of from approximately 1,000 megacycles per second to approximately 10,000 megacycles per second, the rectifier unit provid- Ving-relatively high sensitivity with low noise, and having high burnout capability.

A still further object of the invention is to -provide an improved point-contact rectifier of the type Ycompris- =ingfa 'semi-conductor'material, in the form of a-crystal, `which yis engaged by 'a pointed metallic wire, the Yim- -proved point contact frectifier beingeconomical to manuffa'cture, -providing lhigh conversion gain with low noise, and -being reversible so that it may be reversibly con- "n'ec't'ed to a conventionalcontact socket without requiring "rewiring of the socket or any majormodification of -the `point contact rectifier unit.

-Further lobjects and -advantages -of the invention will become apparent from the following descriptionl and :'claims, and from the accompanying drawings, wherein:

`Figure 1 is a `perspective view of one form of im- .proved point contact rectifier unit constructed in 'accordvance with the -present invention;

Figure 2 is a vertical vcross-sectional view taken on the -line 2-2 Aof -Figure 1;

Figure 3 is a perspective view of a further form -of the improved point contact rectifier unit of the present finvention; and

Figure -4 is a vertical cross-sectional view taken on --the-'line4-4 of Figure 3.

Investigation `of `semiconductor materials has shown thatgermanium is best suited as the material from which .to-construct a point contact crystal rectifierl element for 2,882,466 Patented --Apr. 14, -1959 will yield germanium of a resistivity of approximately 0.004 ohm-centimeter to 0.009 ohm-centimeter, which falls -into'the range ofresistivity required to provide the `necessary 'physical parameters of the'semiconductor, that. inadequate-mobility of minority carriers and bulk resistance, as required in the fabrication and utilization --of the device.

Referring tothe drawings, and more particularly to Figures 1 and2, one form of point contact rectifier unit constructed in accordance with the present invention is designated generally at 11. The rectifier unit 11 comprises a cylindrical sleeve-like ceramic holder 12 which is formedwith internal threads 13 andwhich is formed yat its intermediate portion with a relatively small aperture 14 to allow Athe holder to be filled with wax during the latter stages of fabrication of the rectifier unit, asV will be presently described.

Designatedat 15 is a top conducting terminal which is formed with an externally threaded reduced bottom end 'portion 16 threa'd'edly engageable in the top end ofthe ceramic sleeve "member 12. Designated at 16 is a base contactterminal having a reduced externally threaded portion 17 which is lthreadedly engageable in the lower end of the ceramic sleeve 12, as is clearly shown in Figure 2.

The base contact terminal 16 is formed with the axial, depending contact studelement 18.

.Designated at v19is a vpellet of germanium metalof proper physical characteristics, asdescribed above, the :pellet being cut to a vthickness of approximately 0;015 Vinch and being of suitable shape to fit onto the surfacefof the reduced 'portion 12 of -base contact terminal 16. For example, the pellet 19 may be-square Vand may have Vsides of approximately 0.050 inch in length. The pellet "manufacture lThe top conducting 'terminal `15 Vis formed with an axial bore 20, and ,positioned in -said bore 20 is a'brass Whisker stud,21 which is firmly held in ardesired .-position in ,the bore 20 by a set screw 22 ,provided in-the wall 'of the terminal 15,as is clearly shownin 'Figure-2. The metal wire Whisker, shown -at 23, lconsists-prefer- -ably `of copper wire of'a diameterbetween "01003 cinch and 0.005 inch, ywhich `is formed `,into 'the customary lC-shaped or S-shaped 'Whisker element. ofithe Whisker member 23 fis secured axially Ainthe-ibut- :tom rend ef the-stud member 21 in a'yisuitable fmane'r, as -by `vv'eldin} ,1, solderingor fthe kflike. Thus, an axial The 'top yend recess or bore may befformed in the lower endoffthe 's'tiid 21'into which the fend Akof'the wire member 23 is inserted andi's rigidly isecured, "as by welding or soldering.

The yfree'end o'f'the wire member 23 vis pointed, either "by 'grinding same to form a conical pointed vtip on said free end, orby 'shearing the wire at fan Vangle `ofapproximatelyjO". :,Either method will produce a suitable point,

In the assembly of the point contact rectier`11, the

stud 21 is pushed through the bore 20 until the copper Whisker Wire 23 makes physical contact with the germanium pellet 19. After contact has been made, the stud 21 is pushed inwardly a slight amountV to add sutiicient compression on the metal wire Whisker 23 to insure mechanical stability of the contact between the pointed end of the copper Whisker wire 23 and the germanium pellet 19. To provide for added mechanical stability and moisture protection, the inside of the sleeve member 12 is then llled with suitable insulating material, for example, wax. Thus, the wax is introduced into the ceramic sleeve 12 through the aperture 14, to achieve the desired wax impregnation of the interior of the sleeve member.

Referring now to Figures 3 and 4, the point contact rectifier unit is designated generally at 11' and comprises a cylindrical ceramic sleeve-like body 12' which is internally threaded and which threadedly receives at its lower end the bottom contact terminal 16 and which threadedly receives at its top end the upper contact terminal 15'.

As will be readily apparent from Figure 4, the top and bottom contactterminals 15 and 16 are identical in construction and are respectively formed with the reduced axial shank portions 35 and 36. The respective members 15 and 16' are thus formed with respective annular ange elements 24 and 25 which are located adjacent the top and bottom ends of the ceramic sleeve member 12'.

The two opposite ends of the ceramic body 12 are suitably metalized, for example, are platinumized, to provide metal soldering surfaces at said opposite ends. The flanges 24' and 25 are soldered to the respective top and bottom ends of the body 12 to provide a hermetic seal between the top and bottom members 15' and 16 and the respective top and bottom ends of the ceramic body 12'. Thus, the flanges 24' and 25' are sealed to the top and bottom ends of the ceramic body 12' by respective annular masses of solder, shown at 26' and 27 in Figure 4.

The lower contact terminal 16 is formed with an axial bore 28 in which is located a contact stud 29' having a germanium pellet 19' of proper physical parameters, described above, soldered to its top end. The stud 29' is forced through the bore 28 after the terminal elements 15' and 16 have been hermetically sealed to the top and bottom ends of the ceramic body 12', as above described. A solder seal 30' is then made between the inside surface of the bore 28' and the lower end of the stud 29.

The stud 29 is preferably provided with a lluted external surface so that it will frctionally interengage with the inside surface of bore 28 and become mechanically locked therewith after its has been forced into bore 28' to its desired position.

The upper parallel member 15' is formed with an axial bore 31 in which is positioned a stud member 21', to the lower end of which is secured the copper Whisker wire, shown at 23, said Whisker Wire having a pointed end Which engages the surface of the germanium pellet 19'. In the assembly, the stud 21', carrying the copper Whisker wire 23, is forced through the bore 31 until electrical contact is made between the pointed end of the Whisker 23' and the top surface of the germanium pellet 19. The stud 21' is preferably provided with a longitudinally lluted external surface, similar to that provided on the stud 29', so that the stud 21 will frictionally interengage with the inside surface of bore 31' and will be mechanically locked therewith to provide mechanical stability. A solder seal 32' is made between the inside surface of bore 31' and the top end of the stud 21'.

Designated at 33 is an electrical conducting adapter which may be selectively engaged on the axially projecting outer end portion of either terminal element 15' or terminal element 16' to provide for electrical polarity reversal, whereby the rectier may be reversibly connected to a conventional contact socket. The conductive adapter 33' is coextensive in length with the axially projecting outer end portions of terminals 15' or 16', as is clearly shown in Figure 4.

In the case of both of the modifications above described, after the mechanical assembly is completed, the point contact rectifier unit is preferably electrically formed in the manner described in our copending application Serial No. 630,166, tiled December 24, 1956. This is accomplished by inserting the assembled rectifier unit into a standard mixer which is electrically connected to a conventional electrical device designed to indicate the intermediate frequency impedance and then applying controlled electrical pulses of about one quarter of an ampere to an ampere of a duration of one tenth of a second to a second to the rectifier in the forward direction of the semi-conductor. For the results here desired, the forming current need not be more than one half an ampere. The application of the forming current to the point contact rectifier reduces the intermediate frequency impedance from an initial value of from about 600 to 800 ohms to the required value of between 350 and 450 ohms. During the electrical forming process, current densities ofthe order of several thousand amperes per sq. inch Vare achieved at the pointed end of the Whisker wire, Which in turn produce very high temperatures in the region of contact of the Whisker wire and the germanium pellet. At these elevated temperatures, when a copper or brass wire is used, copper atoms from the Whisker wire diffuse into the n-type germanium. These copper atoms are of acceptor impurity nature, thus forming a small p-n junction in the vicinity of the point contact. By controlling the magnitude of the forming current, the affected area of the junction is controlled, which in turn provides control over the resultant junction capacitance. It is important that this junction capacitance be held to a minimum in the electrical forming process in order to achieve low values of conversion loss, or conversely, high values of conversion gain.

The Whisker wire may be of any suitable metal having the desired physical characteristics, such as platinum, gold, nickel, titanium, or any other suitable metal suitable for operation in the desired portion of the radio frequency spectrum, for example, in the portion of `said spectrum from approximately 1,000 megacycles per second to 10,000 megacycles per second. A wire having substantial copper content is preferable, however, in order to achieve the low enhancement current characteristics described in our aforesaid copending application.

The point contact rectier units of the present invention will operate throughout the radio frequency spectrum from 1,000 megacycles per second to 10,000 megacycles per second in the standard types of mixers now used by the Armed Services and which are approximately designated IAN Approved. At the present time no one type of silicon mixer diode can perform throughout the above cited frequency range. For instance a 1N2l type silicon mixer diode is employed for the range between 1,000 to 4,000 megacycles per second; a 1N150 type silicon mixer diode is employed from 4,000 to 6,000 megacycles per second; and a 1N23 type silicon mixer diode is employed from 6,000 to 10,000 megacycles per second.

While certain specific embodiments of an improved point contact rectifier unit have been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as de -ned by the scope of the appended claims.

What is claimed is: j l. A reversible point contact rectilier for` operation throughout the radio frequency spectrum from 1,000 to 10,000 megacycles per second, comprising. a sleeve-like Vholder of insulating material, a first metallic stud mernber secured in one end of the holder and having an axi ally projecting external shank portion, a germaniumcrys tal element secured on the inner surface of said stud member, a second metallic stud member secured in the opposite end of said holder and having an axially projecting external shank portion identical with the rstnamed shank portion, a copper Wire member secured to the inner end of the second stud member, a point on said wire member engaging and fused with the surface of said crystal element, means hermetically sealing said stud members to the opposite ends of said holder, and a metallic contact sleeve detachably secured on one of said shank portions, said contact sleeve being substantially coextensive in length with said shank portions and Ibeing selectively engageable thereon, whereby the rectifier may be reversibly connected to a contact socket.

2. A reversible point contact rectifier comprising a holder of insulating material, a iirst conductive contact member mounted on one end of said holder, a second conductive contact member mounted on the opposite end of said holder, a semi-conductive crystal element mounted on said first contact member, a Whisker wire mounted on said second Contact member and having an end engaging said crystal member, each of said contact members having a shank portion projecting endwardly from said holder and the shank portions being of the same length and external shape, and a contact sleeve of the 6 same length as, and detachably secured to, one of said shank portions, said sleeve being selectively engageable with either of said shank portions to permit reversal of the rectifier in a socket.

3. A reversible point contact rectifier comprising a tubular holder of insulating material, having opposite ends, a pair of Contact members one mounted on and forming a closure for each of said ends, each of said members having a cylindrical shank portion projecting endwardly from said holder and said shank portions ybeing of the same diameter and length, a semi-conductive crystal element mounted on one of said members and a Whisker wire mounted on the other of said members and engaging said element, and a contact sleeve of the same length as, and detachably secured to, one of said shank portions, said sleeve being selectively engageable with either of said shank portions to permit reversal of the rectifier in a socket.

Kinman Mar. 31, 1953 Jenkins et al July 3, 1956 

